EFFECT OF ESSENTIAL OILS AND PACKAGING ON HOT
SMOKED RAINBOW TROUT DURING STORAGE
PINAR OG˘ UZHAN YILDIZ
Faculty of Engineering, Food Engineering Department, Ardahan University, Ardahan 75000, Turkey
Corresponding author. TEL:+90-478-211-5000 (3020); FAX:+90-478-211-3275;
EMAIL: [email protected] Received for Publication December 18, 2013 Accepted for Publication May 1, 2014 doi:10.1111/jfpp.12291
ABSTRACT
This study investigated the effect of essential oils (EOs) (thyme and rosemary) and packaging (vacuum and modified atmosphere – 50% CO2/+50% N2) on hot
smoking rainbow trout during storage (4C) for 90 days. Fillets were conducted to microbiological (i.e., total aerobic mesophilic bacteria, psychrotrophic bacteria, lactic acid bacteria, Clostridium perfringens, C. botulinum, yeast and mold) and chemical (i.e., pH, thiobarbituric acid reactive substances, total volatile base nitro-gen) analyses and sensory quality on 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90 days. In conclusion, EO treatment to smoking showed positive effect on shelf life, espe-cially thyme oil showed more positive effect when compared with rosemary oil.
PRACTICAL APPLICATIONS
Smoking is one of the oldest methods used for preserving fresh fish and other seafood products. The use of an essential oil in fresh fish preservation may be con-sidered an alternative “natural” additive, extending the shelf life of the product. Our study has clearly shown that addition of rosemary and thyme extract in smoked fish resulted in longer shelf life, and this method could be commercially used.
INTRODUCTION
Microorganisms can grow in the muscle tissue of aquatic products due to their high-nutrient content. So the conser-vation and handling of aquatic products are very important (Babadogan 1998). One of the conservation processes of aquatic products is smoking (Bellagha et al. 2007). Smoking is one of the oldest methods of food preservation and widely used in fish processing (Muratore and Licciardella 2005; Stolyhwo and Sikorski 2005; Yanar et al. 2006; Emir Coban and Can 2013). Smoke is probably the product of incomplete combustion of wood. It consists of numerous individual components, namely, aldehydes, ketones, alco-hols, acids, hydrocarbons, esters, phenols, ethers, etc. These components are transferred to the smoked goods by deposi-tion on their surface and subsequent penetradeposi-tion into their flesh (Doe 1998; Guillen and Errecalde 2002; Goulas and Kontominas 2005). Smoked fish has characteristic flavor and color (Erkan 2012; Emir Coban and Patir 2013). The shelf life of smoked fish products depends largely on the initial bacterial contamination of the raw material, decrease of water activity (aw) in the tissues due to brining and
pre-drying, activation of putrefactive microflora due to heat treatment, amount of smoke components that penetrate the product, and temperature, air humidity and oxygen levels during storage (Sikorski et al. 1990; Ibrahim et al. 2008). There are three methods used to smoke fish: the traditional method by combustion, at either low temperature (cold smoking≤ 30C) or high temperature (hot smoking ≥ 60C); use of a high-voltage electrostatic field that accelerates smoke deposition; and use of liquid smoked fish. Hot smoking is a pasteurizing process, the preservative effect of which depends on the composition and preparation of raw material, temperature, relative humidity, density and com-position of the smoke as well as the smoking time (Goulas and Kontominas 2005). Hot smoking combines in a single process the effects of salting (brining), drying and heating with those of the smoke itself (mainly antioxidant and anti-microbial) (Cakli et al. 2006). Salting process is itself a pres-ervation technique used as a preliminary operation for many processing technology (smoking, drying and marinat-ing processes). The first step of fish smokmarinat-ing process is salting. The main purpose of salting fish meat is the elimi-nation of water. Bacterial activity is largely prevented in
high-salt concentrations. High-salt concentration prevents bacterial activity that can generate spoilage in fish. Conse-quently, salting process significantly increases the shelf life of fish (Ismail and Wootton 1992). Beyond the prevention of microbial growth and reduction of water activity, NaCl is an essential ingredient in processed meat products for its contribution to water-holding capacity, facilitating the solu-bilization of certain proteins and conferring a typical salty taste by enhancing the flavor of such food products (Armenteros et al. 2009). Vacuum packaging method is a type of passive modified atmosphere. After placing the food in a suitable packaging material in this operation, the air in the package is emptied by vacuum and a hermetic closure (air tight) is made. This method is commonly used for pres-ervation of meat products. Even in vacuum packaging a low percentage of O2 remain in the package, and this can be
used by aerobic microorganisms with CO2 production.
These types of products, the bacterial growth and oxidation the product is prevented as air is not in the package (Keles 1998; Gulyavuz and Unlusayin 1999; Kilinc and Cakli 2001). Thus, numerous studies have been conducted on the preser-vation of vacuum on fish and fish products for salmon (Leroi et al. 2000; González-Rodríguez et al. 2002; Martinez et al. 2010), ascidia (Stamatis et al. 2008), sardine (Senesi et al. 1979; Gómez-Estaca et al. 2010) and trout (Schulze 1985; Lyhs et al. 1998; Frangos et al. 2010; Oguzhan and Angis 2012). Modified atmosphere packaging (MAP) is a preservation method use to extend the shelf life of fish and fish products (Ozogul et al. 2006). MAP is the process of eliminating oxygen from inside package and filling with dif-ferent concentrations of CO2and N2; however, refrigerated
storage conditions for aerobic microorganisms, proteolytic bacteria, yeast and mold growth are inhibited (Swiderski et al. 1997; Gulyavuz and Unlusayin 1999; Kilinc and Cakli 2004). There are many MAP studies related to shelf life extension of fish and fishery products for swordfish (Stolyhwo and Sikorski 2005), chub mackerel (Erkan et al. 2007), cod (Cann et al. 1983; Debevere and Boskou 1996), rainbow trout (Cakli et al. 2006; Oguzhan and Angis 2012), salmon (Paludan-Muller et al. 1998), bass (Torrieri et al. 2006), herring (Lyhs et al. 2007) and catfish (Goktepe and Moody 1998). Essential oil (EO) has proven to be an effec-tive preservation method for the extension of shelf life of fresh fish product (Harpaz et al. 2003; Giatrakou et al. 2008; Quitral et al. 2009; Emir Coban et al. 2012; Erkan 2012). EOs are aromatic oily liquids obtained from plant material. Extracts from oregano, thyme, rosemary, clove, sage and mint are some of the EOs that have been used both to improve the sensory characteristics and extend the shelf life of foods. A number of EOs and some of their components have been reported to have antimicrobial activity against a wide range of spoilage and pathogenic bacteria (Lambert et al. 2001; Burt 2004). The aim of this study was to
deter-mine the combined effects of EOs and packaging (vacuum and MAP) on the shelf life of refrigerated (4C) hot smoking rainbow trout fillets by evaluating microbiological and chemical parameters.
MATERIALS AND METHODS
Preparing Samples
Hot smoked fish was prepared from rainbow trout (Oncorhynchus mykiss). Rainbow trout (250± 25 g) were obtained from Ataturk University Agricultural College Fish-eries Department’s Rainbow Trout Breeding and Research Center. The fresh fish samples were carried to laboratory and washed with tap water. A total of 120 fish samples were eviscerated, stored until rigor had resolved and then filleted – 240 fillets in total (Robb et al. 2002). Treatments included C1 (control samples vacuum packaged-hot smoked), C2 (control samples modified atmosphere packaged-hot smoked), R1 (vacuum packaged with added rosemary EO 1% [v/w]), R2 (modified atmosphere packaged with added rosemary EO 1% [v/w]), T1 (vacuum packaged with added thyme EO 1% [v/w]) and T2 (modified atmosphere pack-aged with added thyme EO 1% [v/w]). Each group included 40 fillets.
Brine Salting, EO Treatments and Smoking Process
Salting and EO application processes were made together. Rainbow trout fillets were immersed in brine at a ratio of 1:1 (w/w) containing 20% NaCl for 1 h. Thyme and clove EOs were added to the two lots of filleted samples in appro-priate volumes to the surface (two sides) of each fillet using a micropipette, so as to achieve final 1% (v/w) EO concen-trations. Thyme and clove EOs were added undiluted using a micropipette. In all treatments (given below), the antimi-crobials were massaged onto the product, so as to get even distribution of oil using gloved fingers (to avoid cross-contamination of samples and also transmission of food poisoning organisms).
Then the fillets were dried at 30C for 30 min. After drying, fish were smoked to the smokehouse (Aqua Tech R 137/12). Smoke was produced from oak sawdust with com-bustion. Samples were smoked at 50, 60, 70 and 80C for a total of 2 h for a period of 30 min. Fillets were packed by applying vacuum and modified atmosphere (50% CO2+ 50% N2).
Vacuum and MAP
All filleted samples including the control were packaged in 15× 25 cm thick polyethylene/polyamide (three-seal bags
GB 70) obtained from Südpack Verpackungen GmbH and Co. (Ochsenhausen, Germany), having an O2permeability
of 40 cm3/m2/day atm 23C; N
2permeability of 24 cm3/m2/
day atm 23C; CO2permeability of 145 cm3/m2/day atm 23C;
and water vapor permeability of<3 g/m2/day atm 23C.
After EO process and packaging treatment, rainbow trout fillets were stored under refrigeration (4± 1C) and were subjected to microbiological (total aerobic mesophilic bac-teria, psychrotrophic bacbac-teria, lactic acid bacteria [LAB], yeast and mold) and chemical (pH, thiobarbituric acid reac-tive substances [TBARS], total volatile base nitrogen [TVB-N]) analyses. Microbiological and chemical procedures were performed on 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90 days of storage.
Microbiological Analysis
A sample (25 g) was taken from each group, transferred aseptically into a stomacher bag containing 225 mL of 0.1% peptone water and was homogenized for 60 s in Stomacher (Lab Stomacher Blender 400-BA 7021, Seward Medical, UK) at room temperature. For microbial analyses, 0.1 mL of samples of serial dilutions (1:10, diluent, 0.1% peptone water) was inoculated to proper agar plates. Total meso-philic aerobic bacteria and total psychrotrophic aerobic bacteria were determined on plate count agar (Merck 1.05463.0500, Merck KGaA, Darmstadt, Germany), which were incubated at 30C for 2 days and at 10C for 7 days, respectively. LAB were determined using De Man Rogosa Sharpe agar (Oxoid CM0361), which was incubated at 30C for 2 days. Clostridium perfringens was determined on sulfite polymyxin sulfadiazine agar (Merck 1.10235.0500), which was incubated at 35C for 24 h. C. botulinum used two enrichment media, i.e., cooked meat medium (CMM; Merck) and trypticase peptone glucose yeast extract with trypsin (TPGYT; Merck). CMM was incubated at 35C and TPGYT at 26C for 5 days. Yeast and mold were determined on rose bengal chloramphenicol agar (Merck 1.00467.0500), which was incubated at 25C for 5 days.
Chemical Analysis
TVB-N was determined according to Malle and Tao (1987). TVB-N contents were expressed as mg 100/g fish muscle. TBARS were determined according to the method of Lemon (1975) and Kilic and Richards (2003). TBARS content was expressed asμmol malondialdehyde (MDA)/kg fish muscle. pH was determined according to the method of Gokalp et al. (1999).
Sensory Evaluation
Five experienced panelists, academic staff who were trained in sensory descriptors for smoked fishes, were employed to
evaluate the quality of O. mykiss fillets during storage. The panelists were asked to evaluate the overall acceptability of the appearance, taste and odor of the samples on a 5-point hedonic scale, ranging from very poor (1) to very good (5). All samples were stored at 4C until sensory analysis was performed.
Statistical Analysis
Experiments were replicated twice on two separate occa-sions with different fish samples. Analyses were run in duplicate for each replicate. All obtained data from this study were subjected to analysis of variance followed by Duncan’s multiple range test to determine significant differ-ences among means atα = 0.05 level using SPSS (1999).
RESULTS
Microbiological Changes
Changes in TAMB of refrigerated rainbow trout fillets during storage under vacuum and MAP are shown in Fig. 1a. The initial count (day 0) of TAMB was 2.0 log colony-forming unit (cfu)/g. C1, C2 and R1 exceeded the limit (7 log cfu/g) for fresh marine species (ICMSF 1992) on days 50, 70 and 90 of storage. This limit was not exceeded throughout storage in R2, T1 and T2. At 90 days, C1, C2, R1, R2, T1 and T2 showed 10.36, 9.84, 7.08, 5.23, 6.32 and 4.42 log cfu/g, respectively.
The initial (day 0) psychrotrophic bacteria (Fig. 1b) of rainbow trout fillets was 2.0 log cfu/g. C1, C2 and R1 exceeded the limit (7 log cfu/g) for fresh marine species (ICMSF 1992) on days 50, 80 and 90 of storage. This limit was not exceeded throughout storage in R2, T1 and T2. At 90 days, C1, C2, R1, R2, T1 and T2 showed 10.63, 9.76, 7.14, 5.56, 6.74 and 4.90 log cfu/g, respectively.
LAB (Fig. 1c) showed initial count (day 0) of 2.0 log cfu/g. At the end of storage C1, C2, R1, R2, T1 and T2 reached 9.78, 8.08, 6.17, 5.08, 5.28 and 4.94 log cfu/g, respectively.
C. perfringens and C. botulinum were not detected in any samples. The yeast and mold count (Fig. 1d) was 2.0 log cfu/g at 0 day. At the end of storage C1, C2, R1, R2, T1 and T2 showed 6.05, 5.77, 4.94, 3.64, 3.70 and 3.28 log cfu/g, respectively.
Chemical Changes
TVB-N. The amount of TVB-N is an important criterion
in determining freshness of fish and their products because generally TVB-N values increase according to progression of spoilage process (Kose and Koral 2005). TVB-N is
consists of TMA and ammonia, with the effect of bacteria and endogenous enzymes in fish. TVB-N value is increasing depending on the storage period in preservation fish and fish products (Lannelongue 1980; Oksuztepe et al. 2010). TVB-N values (Fig. 2a) at day 0 were 18.60, 16.63, 18.12, 17.23, 18.28 and 17.74 mg N/100 g for C1, C2, R1, R2, T1 and T2, respectively. C1, C2, R1, R2, T1 and T2 exceeded the limit (25 mg/100 g) for rainbow trout (Robb et al. 2002) on days 20, 30, 60, 70, 70 and 80 of storage, respectively.
Lipid Oxidation. Lipid oxidation is one of the factors
causing spoilage in fish product. Rancidity taste and FIG. 1. TOTAL AEROBIC MESOPHILIC BACTERIA COUNTS (A),
PSYCHROTROPHIC BACTERIA (B), LACTIC ACID BACTERIA COUNTS (C), AND YEAST AND MOLD (D) CHANGES OF TREATMENT WITH THYME AND ROSEMARY ESSENTIAL OIL (1% V/W) ON HOT SMOKING RAINBOW TROUT FILLETS DURING COLD STORAGE IN VACUUM AND MODIFIED ATMOSPHERE PACKAGING CONDITIONS AT 4C
FIG. 2. TOTAL VOLATILE BASE NITROGEN (TVB-N) (A),
THIOBARBITURIC ACID REACTIVE SUBSTANCES (TBARS) (B) AND pH (C) CHANGES OF TREATMENT WITH THYME AND ROSEMARY ESSENTIAL OIL (1% V/W) ON RAINBOW TROUT FILLETS DURING COLD STORAGE IN VACUUM AND MODIFIED ATMOSPHERE PACKAGING CONDITIONS AT 4C
yellow color comprised oxidation product characteristics (Ruiz-Capillas and Moral 2001). Lipid oxidation is a major quality problem especially in fatty marine species. It leads to the development of off-odors and off-tastes in edible oils and fat-containing foods, known as oxidative rancidity. The TBARS value is an index of lipid oxidation measuring MDA content. MDA is formed through hydroperoxides, which are the initial reaction products of polyunsaturated fatty acids with oxygen (Fernandez et al. 1997; Rezaei et al. 2008; Pyrgotou et al. 2010). Initial TBARS values (Fig. 2b) were 2.55, 2.59, 2.25, 2.10, 2.08 and 1.82μmol MDA/kg for C1, C2, R1, R2, T1 and T2, respectively. At the end of storage TBARS values were 11.54, 10.12, 8.18, 6.96, 6.43 and 6.28μmol MDA/kg for treatments C1, C2, R1, R2, T1 and T2, respectively.
pH. pH value of fish meat usually ranges from 5.7 to 6.6.
Fresh fish is close to neutral pH; after death lactic acid will be formed firstly, falling and then rising again with spoilage (Bilgin et al. 2007). The pH values of rainbow trout fillets (Fig. 2c) were 6.29, 6.37, 5.86, 5.62, 5.83 and 5.59 (at initial experiment) and 6.78, 6.57, 6.45, 6.50, 6.21 and 6.27 (at end of storage) for C1, C2, R1, R2, T1 and T2, respectively.
Sensory Changes. The results of the sensory evaluation
(appearance, taste and odor) of smoked rainbow trout samples are presented in Fig. 3a–c. Sensory scores of each sample were at “good quality” after processing. The taste of the C1, C2 and R1 was scored as “spoiled” by the panelists after 50, 60 and 70 days, whereas groups R2, T1 and T2 con-tinued to be scored as good quality. The appearance and odor of thyme extract were much stronger in groups T1 and T2 than in groups R1 and R2; group T2 was mostly pre-ferred by the panelists.
DISCUSSION
Microbial growth and lipid oxidation are factors important to shelf life and consequently to consumer acceptance of fresh meat (Erkan et al. 2011). Control group showed the highest and thyme EO showed the lowest bacteria count. These results showed thyme EO having the greatest antimi-crobial activity. A number of EOs and some of their compo-nents have been reported to have antimicrobial activity against a wide range of spoilage and pathogenic bacteria (Lambert et al. 2001; Burt 2004). Thyme contains high con-centrations of phenolic compounds including carvacrol, thymol, p-cymene and ˠ-terpinene (Marino et al. 1999). The thyme and rosemary oil can be considered effectively inhibitory on the total aerobic flora. The possible synergistic effect of MAP and thyme oil delayed microbial growth and suppressed final counts of spoilage microorganisms in rainbow trout under MAP. Bacterial growth of modified
atmosphere-packaged samples was lower than vacuum-packaged samples, probably due to the presence of CO2gas
in MAP. Carbon dioxide can be considered effectively inhibitory on the total mesophilic and psychrotrophic aerobic bacteria. Similar results were observed by several researchers (Deng et al. 1974; Schulze 1985; Emir Coban 2010; Erkan 2012; Emir Coban and Özpolat 2013). Erkan (2012) reported that thyme and garlic oil treatment was effective in eliminating growth of total aerobic flora. Like-wise, Emir Coban and Özpolat (2013) reported that rose-mary extract was effective in controlling the growth of bacteria. Chouliara et al. (2007) observed that 1% oregano FIG. 3. APPEARANCE (A), TASTE (B) AND ODOR (C) CHANGES OF
TREATMENT WITH THYME AND ROSEMARY ESSENTIAL OIL (1% V/W) ON RAINBOW TROUT FILLETS DURING COLD STORAGE IN VACUUM AND MODIFIED ATMOSPHERE PACKAGING CONDITIONS AT 4C
oil and air packaging treatment reduced the growth of aerobic bacteria in chicken meat. Ozyilmaz (2007) found that thyme EO reduced the growth of psychrotrophic bacteria. Mahmoud et al. (2004) reported that various EOs reduced growth total aerobic mesophilic and psychro-trophic bacteria. Mejlhom and Dalgaard (2002) reported that the combined use of MAP and oregano oil in the pres-ervation of cod fillets retarded the growth of aerobic micro-organisms, during refrigeration storage (2C).
LAB are facultative anaerobic bacteria that can grow under both anaerobic and aerobic conditions (Plahar et al. 1991). Similar results were found for hot smoking fish by Emir Coban (2010), Erkan (2012) and Emir Coban and Özpolat (2013). Giatrakou et al. (2008) and Kykkidou et al. (2009) reported that thyme–oregano oil treatment was effective in eliminating the growth of TVC and LAB in modified atmosphere-packaged fish under refrigerated storage. Kostaki et al. (2009), Pournis et al. (2005) and Stamatis and Arkoudelos (2007) observed that thyme oil treatment did not reduce the growth of LAB.
C. perfringens and C. botulinum were not detected in any samples. Similar results were found for smoked mussels by Sengor et al. (2004). Eklund (1982) reported that sodium chloride, sodium nitrite, liquid smoke and other preserva-tives prevented C. botulinum survival.
Yeast and mold counts in control groups were higher than EO-treated groups. These results showed the antifun-gal activity of EOs. Similar yeast and mold (day 0) were reported for hot smoking fish by Emir Coban (2010) and Emir Coban and Özpolat (2013). Ozyilmaz (2007), Rasooli and Owlia (2005) and ve Karaman et al. (2001) observed that thyme treatment reduced yeast–mold counts.
TVB-N is one of the most widely used indices of fish quality. Its increase is related to the activity of spoilage bac-teria and endogenous enzymes (Ozogul et al. 2004; Ruiz-Capillas and Moral 2005; Pyrgotou et al. 2010; Erkan et al. 2011). According to quality classification, in “very good” TVB-N value should be up to 25 mg/100 g, “good” up to 30 mg/100 g, “marketable” up to 35 mg/100 g and “spoilaged” more than 35 mg/100 g were evaluated (Varlik et al. 1993). The TVB-N values of rainbow trout fillets were 18.60, 16.63, 18.12, 17.23, 18.28 and 17.74 mg N/100 g (at initial experiment) and 40.18, 39.39, 35.3, 29.08, 32.47 and 28.79 (at end of storage) for C1, C2, R1, R2, T1 and T2, respectively. These values increased in the duration of storage time in all groups. TVB-N values in control groups were higher than EO-treated groups. These increases can be explained by proteolysis due to enzymatic and microbial activities in the samples during processing. Similarly, TVB-N values have been reported for rainbow trout (Erkan 2012). Goulas and Kontominas (2007) found that TVB-N values in EO-treated groups were lower than control
groups. Very little information is available in the literature on the effect of EOs on the TVB-N production in fish. The inhibition of TVB-N production in four and six groups smoked rainbow trout samples may be attributed to the effects of MAP and/or with the combined synergistic effect of thyme and rosemary oil, the latter known to possess anti-bacterial properties due to its phenolic (carvacrol and thymol) and organosulfur (allicin) constituents (Burt 2004).
The consumability limit value of the TBA content was between 7 and 8 mg/MDA kg (Sinnurber and Yu 1958; Emir Coban and Özpolat 2013). In “perfect material” TBA value should be less than 3 mg MDA/kg, in “good material” TBA value should not be more than 5 mg MDA/kg and con-sumption limit for TBA value is between 7 and 8 mg MDA/ kg. TBA values showed the degree of rancidity in the products, and values greater than 3–4 mg MDA/kg indi-cated loss of product quality (Frangos et al. 2010). These values increased in the duration of storage time in all groups. The lowest TBARS values were obtained from the group treated with EOs. These results showed the antioxi-dant characteristics of EOs. Similar results have been obtained in the literature on the effective antioxidant activ-ity of EOs in rainbow trout (Emir Coban 2010; Erkan 2012) and pike (Emir Coban and Özpolat 2013). Fernandez-Lopez et al. (2005) found that TBA values in EO-treated groups were lower than control groups. Serdaroglu and Felekoglu (2005) observed that rosemary and onion extract inhibited TBA. The use of thyme oil to protect muscle foods against oxidation has been reported in the literature. Mariutti et al. (2008) and Erkan and Bilen (2010) observed that garlic oil and thyme oil was an effective means of controlling lipid oxidation in chicken and fish meat, as reflected in TBARS values. Kykkidou et al. (2009) observed that the combined use of thyme oil and MAP did not significantly affect LAB population in swordfish fillets. The limited action of EOs is attributed to the high tolerance of LAB to the action of the oils, due to their ability to generate ATP and to deal with conditions of osmotic stress (Burt 2004).
The pH in fresh fish flesh is almost neutral. In the post-mortem period, decomposition of nitrogenous compounds leads to an increase in pH in fish flesh. The increase in pH indicates the loss of quality (Can 2011). Similar findings were reported by other researchers (Goulas and Kontominas 2007; Emir Coban 2010; Erkan 2012). pH values of modi-fied atmosphere-packaged group were lower than vacuum-packaged samples. This result occurred due to carbonic acid conversion of carbon dioxide.
The taste of the C1, C2 and R1 was scored as spoiled by the panelists after 50, 60 and 70 days, whereas groups R2, T1 and T2 continued to be scored as good quality. The appear-ance and odor of thyme extract were much stronger in groups T1 and T2 than in groups R1 and R2; group T2 was
mostly preferred by the panelists. The use of rosemary and thyme EOs improved the sensory quality of smoked prod-ucts. Similar results have been reported in other recent studies (Emir Coban 2010; Ucak et al. 2011; Erkan 2012; Emir Coban and Özpolat 2013).
In conclusion, EO treatment to smoking showed positive effect on shelf life, especially clove oil showed more positive effect when compared with thyme oil. In the present study, usage of these EOs in smoked fish showed positive effect on the product’s chemical and microbial attributes. Overall, the combined use of thyme EO (1%, v/w) and MAP showed a synergistic effect for shelf life extension of rainbow trout fillets.
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